/**
 * NFS
 *
 * Contacted you to write a program that reads a single tree 
 * circumference (C) and prints the corresponding diameter (D) 
 * of the tree 
 *
 * This program is released to public domain according to
 * author's wish, you can view full license at
 * http://tomatoeskit.org/upload/PublicDomainLicense.txt
 *
 * @author Fangning CHENG (Alpha.L Cheng) <chengf@purdue.edu>
 *
 * @lab section number 
 *
 * @date Aug 30, 2013
 *
 */

import java.util.Scanner;
import java.io.PrintStream;


public class NFS {

	public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in); // A Scanner Obj
        double circumference; // circumference of forest
        circumference = scanner.nextDouble();
        scanner.close();
        PrintStream printStream = new PrintStream(System.out);
        printStream.printf("%.2f\n",circumference / Math.PI);
        printStream.close();
	}

}
